feat(mise): Generate toolbox conf.d files dynamically from tools.yaml

Toolboxes declared in .chezmoidata/tools.yaml no longer need a matching
source file under private_dot_config/mise/conf.d/. The run_onchange
install script now loops over tools.yaml/hosts.yaml directly to
(re)generate ~/.config/mise/conf.d/<toolbox>.toml, and removes files for
toolboxes no longer assigned to the host/user, so mise config.toml stays
limited to individual, non-toolbox tools.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01GA4dAzARMnLz1G9AmQkYYn

private_dot_config/mise/config.toml.tmpl

@@ -35,7 +35,8 @@ chezmoi = "latest"
 neovim = "latest"
 tree-sitter = "latest"
 
-# Tools automated with chezmoi
+# Individual tools automated with chezmoi
+# (toolboxes from .chezmoidata/tools.yaml live in ~/.config/mise/conf.d/<toolbox>.toml)
 {{ includeTemplate "mise-tools" . }}
 
 # Password managers